Effects of Oxidation on the Fatigue Crack Growth Resistance and the Interfacial Properties of a Ti-MMC Laminate Composite

Fatigue crack growth rates in a [0/90](2s) Ti-6Al-4V/SCS-6 cross-ply laminate, correlated with push-out tests, have been measured to assess the effects of varying test temperature, environment, load ratio (R), and initial stress intensity factor range (DeltaK). The fatigue crack growth resistance is degraded in tests at 450 degreesC in air, but tests carried out at test temperatures of up to 450 degreesC under vacuum, both at R = 0.1 and R = 0.5, have shown crack arrest/catastrophic failure transitions (CA/CF), which are similar to those observed for specimens studied at room temperature and at 300 degreesC in air. Moreover, for such [0/90] composites, the critical role of intact 0 deg fibers bridging in the crack wake, in promoting fatigue crack growth resistance, has been confirmed. Sudden increases of fatigue crack growth rate can be attributed to individual fiber failure(s), which were detected by acoustic emission techniques. The effect of the experimental conditions (environment, test temperature, and duration) on the mechanical behavior (fatigue crack growth rate, push-out tests, and broken fibers pull-out lengths) of this laminate may be explained by the modification of the interfacial zone (decrease in the carbon layer thickness due to oxidation and formation of TiO2).